Binocular visual field (VF) loss is linked to an increased likelihood of car accidents. Yet, little is known about the location and type of VF defect that is most likely to affect driving performance. This study employed a novel gaze-contingent display to test the hypothesis that location of VF loss is important when considering impact on performance on the driving Hazard Perception Test (HPT).

Methods

The HPT is a required component of the UK driving exam for new drivers. The computer-based test measures response rate for detecting hazards (events that cause the driver to take action) in a set of real-life driving films. A HPT score out of 75 is calculated based on the efficiency of detecting 15 hazards in 14 films (pass mark=44). Thirty UK drivers with healthy vision completed three versions of the HPT in random order. In two versions, a computer set-up incorporating a Tobii TX300 eye-tracker (Tobii, Danderyd, Sweden) modified the position of a distortion in the image that coincided with the simulated position of a VF defect; this was done in the superior (Fig b) and inferior (Fig c) VF respectively according to the user’s real-time gaze as they completed the HPT. The other version was unmodified to measure baseline performance.

Results

Participants scored 49/75 on average (standard deviation [SD]=9) when the films were unmodified. Mean (SD) performance fell by 18% [40(11)] when viewing films with a superior defect, and 12% with an inferior defect [43(10)]. A repeated-measures ANOVA tested within-person differences in performance and the main effect was significant (p<0.001). Pairwise comparisons for superior versus inferior defects were statistically significant (p=0.01; 95% CI for mean difference=1 to 7).

Conclusions

In this study, simulated VF defects impaired ability to detect driving hazards relative to participants’ normal performances. Superior VF defects were more detrimental for hazard detection than inferior defects. These results could inform the design of better tests of the VF component for fitness to drive.

Participants completed 3 versions of the HPT on a computer set-up incorporating an eye tracker. One version was unmodified to measure baseline performance (a). In the other blocks, a simulated defect, scaled in size to a binocular VF covering 24 degrees, moved according to the person’s gaze position (red dot) in the superior (b) and inferior (c) VF respectively. Grayscales of the binocular VFs are also shown.

Participants completed 3 versions of the HPT on a computer set-up incorporating an eye tracker. One version was unmodified to measure baseline performance (a). In the other blocks, a simulated defect, scaled in size to a binocular VF covering 24 degrees, moved according to the person’s gaze position (red dot) in the superior (b) and inferior (c) VF respectively. Grayscales of the binocular VFs are also shown.